As is known, in spinning processes, a sliver is an intermediate product which appears for the first time after a card. This sliver is generally effective as a feed material or for further processing in subsequent spinning machinery. In order to prepare the sliver for a spinning machine which produces yarn, the discrete sliver fibers must be aligned lengthwise and parallel to one another. Usually, this is achieved by giving the sliver one or more drafting treatments or by combing out of the sliver on a comber followed by drafting.
The cohesion length of the resulting sliver is smaller in proportion as the fibers are aligned more parallel to one another since the cohesion length depends upon the coefficient of friction between the discrete fibers. However, the tendency for a sliver to tear, particularly on a relatively long feed path to a subsequent machine, increases in proportion as the fibers are aligned more parallel to one another. This is disadvantageous for subsequent processing. For example, yarn count errors may arise at restarting and the machine may have to be stopped.
German OS 3,610,212 discloses a construction wherein a number of pairs of pressing rollers are disposed after a drawframe with the aim of providing additional compression of the sliver. The purpose of this step is to increase the quantity of sliver which can be deposited in a can without the sliver in the can experiencing pressure. This pressing-together of the fibers briefly increases the friction between them and, therefore, the cohesion length. However, upon release of the pressure on the sliver, the cohesion length returns to a value little higher than before the pressing step.
German OS 3,319,514 discloses a pair of toothed rollers for conveying a sliver. Tooth height is relatively large so that the sliver can escape. Also, the teeth of the two rollers must be accurately aligned relatively to another if the fibers are not to be damaged.
Calendaring mechanisms have also been known from U.S. Pat. No. 3,328,851 which employ a pair of fluted rollers and means including a tension spring for resiliently maintaining a desired nip-spacing between the rollers during normal operation while permitting enlargement of such spacing in response to the occurrence of a lap-up condition or other increase in the thickness of the strand material within the mechanism at any given point in time.
Other types of conveying arrangements have also been known wherein a sliver is passed between a pair of fluted rollers such as described in German OS 3319514 and OS 2609615. Other types of arrangements are also from French Patent No. 2,601,661 for biasing a pair of smooth calendar rollers towards each other for compressing a sliver.
Accordingly, it is an object of the invention to provide a relatively simple device for increasing the cohesion length of sliver.
It is another object of the invention to provide a relatively simple structure for imparting increased cohesion length to a sliver for conveyance to subsequent processing stages.
It is another object of the invention to be able to increase the cohesion length of a sliver without damaging the fibers of the sliver and without imparting any detrimental characteristic to the sliver for subsequent processing.